Suppose FIGURE 31-42 shows an electron in an atom that is orbiting a nucleus counterclockwise (that is, the charge is moving to the right at the moment pictured in the diagram). The indicated magnetic field has just been turned on from an initial value of zero. 

(a) Treating the electron as a circular ring of electric current, use Faraday's law to determine whether the electron will speed up or slow down in response to turning on the magnetic field. 

(b) The circulation of the electron produces a magnetic field at the center of its orbit. Will the magnitude of its magnetic field increase or decrease in response to turning on the external magnetic field?

(c) Does the magnetic field produced by the orbiting electron point in the same direction as the external magnetic field, or in the opposite direction? (This question offers a crude explanation for the effect of diamagnetism, presented in Chapter 22.)

Figure 31-42

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